The present invention relates generally to pressure monitoring systems of the purge gas type in which purge gas is injected into media to facilitate measurement of media pressure and other parameters.
In purge gas pressure monitoring systems, a piezometer tube runs from a pressure measuring instrument into a medium to be monitored. Purge gas is supplied to the tube to escape as bubbles at the end of the tube submerged in the medium. The pressure of gas escaping from the tube is a function of the pressure of the medium into which it is bubbled, and the bubble gas pressure can be monitored by a suitable pressure-responsive instrument such as a pressure transducer or balanced beam manometer device. The output from the instrument is provided to a suitable output device for providing a visual indication of the pressure. The output device may be a suitable data recorder such as an electronic data logger or a video display screen.
Such systems are subject to various errors which cause inaccuracies in the results. The purge gas technique is subject to gas weights errors due to the vertical weight of gas in the bubbler tube, as described in U.S. Pat. No. 5,005,408 of Glassey. It is also subject to errors as a result of temperature variations. Some errors are inherent in the type of pressure-responsive instrument used. For example, spring-opposed pressure transducers must be compensated for variations of Earth gravity, and are also subject to errors as a result of change in temperature of the transducer case and/or body.
Attempts have been made in the past to compensate for some of these errors. However, these have been typically applied to a specific pressure-responsive instrument and have been inconvenient to use in some cases.